Re-land "Check in a simple pure-python based Markdown previewer."

third_party/Python-Markdown/markdown/blockparser.py

+from __future__ import unicode_literals
+from __future__ import absolute_import
+from . import util
+from . import odict
+
+
+class State(list):
+    """ Track the current and nested state of the parser.
+
+    This utility class is used to track the state of the BlockParser and
+    support multiple levels if nesting. It's just a simple API wrapped around
+    a list. Each time a state is set, that state is appended to the end of the
+    list. Each time a state is reset, that state is removed from the end of
+    the list.
+
+    Therefore, each time a state is set for a nested block, that state must be
+    reset when we back out of that level of nesting or the state could be
+    corrupted.
+
+    While all the methods of a list object are available, only the three
+    defined below need be used.
+
+    """
+
+    def set(self, state):
+        """ Set a new state. """
+        self.append(state)
+
+    def reset(self):
+        """ Step back one step in nested state. """
+        self.pop()
+
+    def isstate(self, state):
+        """ Test that top (current) level is of given state. """
+        if len(self):
+            return self[-1] == state
+        else:
+            return False
+
+
+class BlockParser:
+    """ Parse Markdown blocks into an ElementTree object.
+
+    A wrapper class that stitches the various BlockProcessors together,
+    looping through them and creating an ElementTree object.
+    """
+
+    def __init__(self, markdown):
+        self.blockprocessors = odict.OrderedDict()
+        self.state = State()
+        self.markdown = markdown
+
+    def parseDocument(self, lines):
+        """ Parse a markdown document into an ElementTree.
+
+        Given a list of lines, an ElementTree object (not just a parent
+        Element) is created and the root element is passed to the parser
+        as the parent. The ElementTree object is returned.
+
+        This should only be called on an entire document, not pieces.
+
+        """
+        # Create a ElementTree from the lines
+        self.root = util.etree.Element(self.markdown.doc_tag)
+        self.parseChunk(self.root, '\n'.join(lines))
+        return util.etree.ElementTree(self.root)
+
+    def parseChunk(self, parent, text):
+        """ Parse a chunk of markdown text and attach to given etree node.
+
+        While the ``text`` argument is generally assumed to contain multiple
+        blocks which will be split on blank lines, it could contain only one
+        block. Generally, this method would be called by extensions when
+        block parsing is required.
+
+        The ``parent`` etree Element passed in is altered in place.
+        Nothing is returned.
+
+        """
+        self.parseBlocks(parent, text.split('\n\n'))
+
+    def parseBlocks(self, parent, blocks):
+        """ Process blocks of markdown text and attach to given etree node.
+
+        Given a list of ``blocks``, each blockprocessor is stepped through
+        until there are no blocks left. While an extension could potentially
+        call this method directly, it's generally expected to be used
+        internally.
+
+        This is a public method as an extension may need to add/alter
+        additional BlockProcessors which call this method to recursively
+        parse a nested block.
+
+        """
+        while blocks:
+            for processor in self.blockprocessors.values():
+                if processor.test(parent, blocks[0]):
+                    if processor.run(parent, blocks) is not False:
+                        # run returns True or None
+                        break